Page 171 - For Men of Understanding

The above illustration
shows the twelve
factors beneficial to
birds while flying:
1. The sun,
2. Sense of timing,
3. Location of the stars,
4. Ultraviolet rays,
5. Polarised light,
6. Sounds of very low
frequency,
7. Sounds such as of
waves and thunder
coming from very far
away,
8. The magnetic field of
the earth,
9. Gravity,
10. Meteorological
assessment,
11. Favourable winds,
12. Characteristics of
the ground below.

A PERFECT SENSE OF HEARING

During migration, birds also take atmospheric phenomena into considera-
tion. For instance, they change direction to avoid a coming storm. Melvin L.
Kreithen, an ornithologist who made research into birds’ sense of hearing,
observed that some birds can hear sounds of extremely small frequencies,
which diffuse to great distances in the atmosphere. A migratory bird can there-
fore hear a storm breaking out over a far away mountain or thunder over an
ocean hundreds of kilometres ahead. Besides, it is a known fact that birds are
careful to set their routes of migration away from regions where atmospheric
conditions are risky.

PERCEPTION OF DIRECTION
How do birds find their direction without the help of a map, a compass or

some similar direction finder during their thousands of kilometres long flights?
The first theory put forward regarding this question was that birds memo-
rise the characteristics of the ground beneath them and thus reach their desti-
nation without being confused. Yet, experiments have shown that this theory
is incorrect.
In an experiment on pigeons addressing this subject, opaque lenses were
used to blur the vision of pigeons. Thus, they were prevented from navigating
by landmarks on the ground, yet the pigeons could still find their way even if
left some kilometres away from their flocks.
Subsequent research has shown that the magnetic field of the earth seems
to act on bird species. Various studies have shown that birds have seemingly

The Signs in Living Things 169